Gas delivery system for reducing oxidation in wire bonding operations

ABSTRACT

A wire bonding machine is provided. The wire bonding machine includes a bonding tool and an electrode for forming a free air ball on an end of a wire extending through the bonding tool where the free air ball is formed at a free air ball formation area of the wire bonding machine. The wire bonding machine also includes a bond site area for holding a semiconductor device during a wire bonding operation. The wire bonding machine also includes a gas delivery mechanism configured to provide a cover gas to: (1) the bond site area whereby the cover gas is ejected through at least one aperture of the gas delivery mechanism to the bond site area, and (2) the free air ball formation area.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of the U.S. patent application Ser.No. 12/739,100 filed on Apr. 21, 2010, which claims the benefit ofInternational Application No. PCT/US2009/046535 filed on Jun. 8, 2009which claims the benefit of U.S. Provisional Application No. 61/060,189,filed Jun. 10, 2008, the contents of which are incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates to wire bonding of semiconductor devices,and more particularly, to providing a cover gas to certain areas of awire bonding machine.

BACKGROUND OF THE INVENTION

In the manufacturer of various semiconductor devices, wire bondingtechniques are often used to connect components in the devices. Forexample, wire bonds (or wire loops) are often used to provideinterconnection between a semiconductor die and contacts on a leadframe.An exemplary conventional wire bonding operation involves (1) bonding afree air ball to a first bonding location on a die (e.g., using ballbonding) to form a first bond, (2) extending a wire from the first bondtoward a second bonding location on a leadframe, (3) bonding the end ofthe extended wire to the second bonding location to form a second bond,and (4) cutting the wire. In such a ball bonding operation, anelectronic flame off (i.e., EFO) wand/electrode or the like is typicallyused to form the free air ball at the end of the wire at step (1).

Often, gold wire (which is substantially non-reactive with oxygen) isused in wire bonding processes; however, in certain applications, morereactive metals (e.g., copper, silver, palladium, aluminum, etc.) areused. These more reactive metals may react, for example, in the presenceof oxygen and form oxides/oxidation on the wires (and/or wire ends ortails) which are undesirable for wire bonding.

In view of such potential oxidation, certain wire bonding systemsinclude subsystems for providing a cover gas to the end of a wire duringformation of the free air ball by the EFO wand. For example, U.S. Pat.No. 6,234,376, which is incorporated by reference in its entirety,discloses such a system.

Additionally, various subsystems of wire bonding machines are used toprovide the cover gas to the bond site area of the wire bonding machineto reduce the potential for oxidation of the bonding wire in the bondsite area. Exemplary subsystems for providing a cover gas in the bondsite area include U.S. Patent Application Publication Nos. 2007/0284421;2007/0251980; and U.S. Pat. Nos. 5,265,788; 5,395,037; 6,866,182; and7,182,793.

It would be desirable to provide improved structures for reducingoxidation in wire bonding.

SUMMARY OF THE INVENTION

According to an exemplary embodiment of the present invention, a wirebonding machine is provided. The wire bonding machine includes a bondingtool and an electrode for forming a free air ball on an end of a wireextending through the bonding tool where the free air ball is formed ata free air ball formation area of the wire bonding machine. The wirebonding machine also includes a bond site area for holding asemiconductor device during a wire bonding operation. The wire bondingmachine also includes a gas delivery mechanism/system (e.g., a gasdelivery structure) configured to provide a cover gas to: (1) the bondsite area whereby the cover gas is ejected through at least one apertureof the gas delivery mechanism to the bond site area, and (2) the freeair ball formation area.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is best understood from the following detailed descriptionwhen read in connection with the accompanying drawing. It is emphasizedthat, according to common practice, the various features of the drawingare not to scale. On the contrary, the dimensions of the variousfeatures are arbitrarily expanded or reduced for clarity. Included inthe drawing are the following figures:

FIG. 1A is a perspective view of a portion of a wire bonding system inaccordance with an exemplary embodiment of the present invention;

FIG. 1B is a detailed view of a portion of FIG. 1A;

FIG. 1C is a perspective view of a gas delivery mechanism including acover for covering a portion of a window of a device clamp in accordancewith an exemplary embodiment of the present invention;

FIG. 1D is a top detailed view of a portion of FIG. 1A;

FIG. 1E is a top view of a portion of the gas delivery mechanism for thewire bonding machine of FIG. 1A in accordance with an exemplaryembodiment of the present invention;

FIG. 1F is a front view of a portion of FIG. 1G taken along line 1F-1F;

FIG. 1G is a perspective view of a bottom portion of a housing of thegas delivery mechanism for the wire bonding machine of FIG. 1A with aninsulator adjacent a tip end portion of an electrode in accordance withan exemplary embodiment of the present invention;

FIG. 1H is a perspective view of a bottom portion of a housing of thegas delivery mechanism for the wire bonding machine of FIG. 1A withoutan insulator adjacent a tip end portion of an electrode in accordancewith an exemplary embodiment of the present invention;

FIG. 2 is a top perspective view of a portion of another gas deliverymechanism in accordance with an exemplary embodiment of the presentinvention;

FIG. 3 is a top perspective view of a portion of yet another gasdelivery mechanism in accordance with an exemplary embodiment of thepresent invention;

FIG. 4A is a top perspective view of a portion of yet another gasdelivery mechanism in accordance with an exemplary embodiment of thepresent invention;

FIG. 4B is a bottom perspective view of the portion of the gas deliverymechanism of FIG. 4A;

FIG. 5A is a front perspective view of elements of a wire bondingmachine including gas delivery mechanism elements in accordance with anexemplary embodiment of the present invention;

FIG. 5B is a bottom perspective view of the elements of FIG. 5A;

FIG. 5C is a front view of the elements of FIG. 5A;

FIG. 6A is a front perspective view of a portion of a gas deliverymechanism integrated with certain components of a wire bonding machinein accordance with an exemplary embodiment of the present invention;

FIG. 6B is a side perspective view of a portion of the gas deliverymechanism of FIG. 6A;

FIG. 6C is a top view of a portion of the gas delivery mechanism of FIG.6A with certain internal details shown in hidden lines;

FIG. 6D is a cut-away front perspective view of a portion of the gasdelivery mechanism of FIG. 6A;

FIG. 7A is a front perspective view of a portion of a gas deliverymechanism integrated with certain components of a wire bonding machinein accordance with an exemplary embodiment of the present invention;

FIG. 7B is a side perspective view of a portion of the gas deliverymechanism of FIG. 7A;

FIG. 7C is a top view of a portion of the gas delivery mechanism of FIG.7A with certain internal details shown in hidden lines;

FIG. 7D is a bottom perspective view of a portion of the gas deliverymechanism of FIG. 7A; and

FIG. 7E is a cut-away front perspective view of a portion of the gasdelivery mechanism of FIG. 7A.

DETAILED DESCRIPTION OF THE INVENTION

U.S. Pat. No. 6,234,376, as well as United States Patent PublicationNos. 2007/0284421 and 2007/0251980, relate to oxidation reductionsystems for wire bonding technology, and are herein incorporated byreference in their entirety.

As is understood by those skilled in the art, the bond site area refersto the portion of a wire bonding machine where the actual formation ofwire bonds (i.e., bonding or welding a portion of a wire to a bondinglocation) occurs. For example, a leadframe strip carrying devices may besupported by a heat block of the wire bonding machine, and may besecured by a clamp of the wire bonding machine, during a wire bondingoperation. In such a case, during wire bonding, the portion of theleadframe/devices accessible through a device aperture(s) of the windowclamp may be viewed as the bond site area. Further, as is understood bythose skilled in the art, the free air ball formation area is thelocation where free air balls are formed during wire bonding. Such alocation tends to be defined by other components including the locationof the tip of an electrode for forming the free air balls, the locationof the bonding tool, the location/length of the wire extending from thebonding tool, etc. (which locations may differ or be altered frommachine to machine).

The present invention relates to gas delivery mechanisms/systems thatintegrate a cover gas (e.g., a forming gas) flow into each of (1) theelectronic flame-off area where free air balls are to be formed (i.e.,the free air ball formation area), and (2) the bond site area. Incertain embodiments, an EFO electrode is positioned at least partiallywithin the gas delivery system without interfering with gas flow toeither of the locations. The cover gas provided to the EFO area reducesthe potential for oxidation during free-air-ball formation (e.g., duringfree air ball formation of copper wire) while the cover gas provided tothe bond site area reduces the potential for oxidation of the wireduring the bonding operation. By providing cover gas to the free airball formation area and the bond site area using a singlemechanism/structure, a number of advantages are achieved. For example, asimple cost effective mechanism is provided. Additionally, visibilityand access during the wire bonding operation are facilitated by thereduction of multiple structures on the wire bonding machine. Furtherstill, a desirable range of motion for the bond head may be facilitatedin contrast to other arrangements.

According to certain exemplary embodiments of the present invention, agas (e.g., a cover gas such as a gas including nitrogen, argon, etc.)(where the gas may or may not include a reducing gas such as hydrogen)is provided: (1) in the vicinity of the electronic flame off operationof a wire bonding machine; and (2) in the vicinity of the bond site areaof a wire bonding machine. For example, during a wire bonding operation,a constant (or variable or controlled) supply of the gas may beprovided: (1) in the vicinity of the electronic flame off operation of awire bonding machine; and (2) in the vicinity of the bond site area of awire bonding machine, such that during the wire bonding operation thereis a reduced potential for oxidation of the wires. Depending upon thegas (and temperature) used, there may also be a reduction ofoxide/oxidation already present on the wires, similar to the effect ofapplying a reducing gas during formation of a free air ball.

For example, during formation of free air balls used during ballbonding, it is desirable to provide a cover gas to reduce the potentialfor oxidation of the wire/free air ball because such oxidation mayresult in an undesirable wire bond and the like. Further, during a wirebonding operation, after completing a wire loop (and prior to formingthe next free air ball) a wire tail (e.g., the end portion of wiresuspended from a capillary tip) may be subjected to oxygen or the likeresulting in oxides forming on the wire tail. Such oxides may beundesirable for bonding, even if the wire tail is later formed into afree air ball. Of course, there are other phases of the wire bondingoperation during which it is desirable to reduce the potential foroxidation of the wire (and/or wire ends) such as, for example, (1) whenforming the second bond in the bond site area, (2) when lowering aformed free air ball to the bond site area, amongst others. The presentinvention addresses these situations by providing a supply of the gas:(1) in the vicinity of the electronic flame off operation of a wirebonding machine; and (2) in the vicinity of the bond site area of a wirebonding machine.

FIG. 1A illustrates wire bonding machine 10 (with various componentsremoved for simplicity). Wire bonding machine 10 includes bond headassembly 100 which includes various components which are moved (e.g.,using an XY table of the wire bonding machine) to form wire loopsbetween bonding locations. Wire bonding machine 10 also includes deviceclamp 102 (sometimes referred to as a window clamp or a clamp insert)which secures the device to be wire bonded into place (e.g., on a heatblock of the wire bonding machine). Referring now to the detailed viewprovided in FIG. 1B, various elements carried by bond head 100 areillustrated including transducer 104 and bonding tool 106. Also shown isgas delivery mechanism 110, through which bonding tool 106 extends. Morespecifically, bonding tool 106 extends through aperture 110 c of gasdelivery mechanism 110. Bonding tool 106 is used to form wire loopinterconnects between bonding locations. The bonding locations are partof bond site area 108 which is accessible to bonding tool 106 throughdevice aperture 102 a (also known as a window) of device clamp 102. Aswill be explained in greater detail below, gas delivery mechanism 110 isused to provide a gas (e.g., a cover gas) to (1) the vicinity of theelectronic flame off operation of a wire bonding machine, and (2) thevicinity of the bond site area of a wire bonding machine. As shown inFIG. 1B, in this example gas delivery mechanism 110 is supported by EFO(electronic flame-off) electrode support structure 100 a, which iscarried by the XY table of wire bonding machine 10.

FIG. 1C illustrates an exemplary embodiment of the present invention inwhich cover 112 is provided over a portion of device aperture 102 a ofdevice clamp 102. For example, cover 112 may be secured to gas deliverymechanism 110 (or some other portion of EFO electrode support structure100 a) such that cover 112 is presented (e.g., by XY table motion) tocover a portion of device aperture 102 a, thereby reducing the rate atwhich the cover gas escapes bond site area 108 (thereby saving cover gascosts, and improving the usefulness of the cover gas in reducing thepotential for oxidation of portions of the bonding wire).

FIG. 1D is a cross sectional perspective view of gas delivery mechanism110 illustrating a portion of cavities 110 a and 110 b of gas deliverymechanism 110. In FIG. 1D, bonding tool 106 is shown in a bondingposition where the tip end of the bonding tool is used to bond a portionof wire (not shown) to bonding locations in bond site area 108; however,it is understood that in a free air ball forming position, bonding tool106 is raised (in comparison to the view of FIG. 1D) such that the tipend portion of bonding tool 106 is within/adjacent gas deliverymechanism 110. In such a position, an electronic flame off wand (shownin FIGS. 1G and 1H) is used to form a free air ball on an end of a wireextending from the tip end of bonding tool 106. Because the free airball is formed within/adjacent a gas filled cavity of gas deliverymechanism 110 the free air balls may be formed in an environment with areduced potential for oxidation.

Gas delivery mechanism 110 may include a top portion and a bottomportion which collectively define cavities 110 a and 110 b. FIG. 1Eillustrates internal portions of gas delivery mechanism 110 (i.e., thetop of gas delivery mechanism 110 is transparent in the illustration).Gas delivery mechanism 110 defines cavity 110 a and cavity 110 b. Cavity110 a defines a gas delivery path between (1) a first gas inlet 114(e.g., a gas supply pipe or tube 114), and (2) the vicinity of theelectronic flame-off operation. More specifically, as shown in FIG. 1Eby the arrows, gas flow (e.g., a controlled gas supply) is provided tofirst gas inlet 114. The gas flows from first gas inlet 114 along thepath provided by cavity 110 a. The path provided by cavity 110 a extendsto the area where free air balls are to be (i.e., the vicinity of theelectronic flame-off operation, also known as the free air ballformation location). As shown in FIG. 1E, electrode 118 (i.e., anelectrode of an electronic flame-off device used to form free air balls)extends through gas delivery mechanism 110 such that the tip ofelectrode 118 terminates within cavity 110 a. As is known to thoseskilled in the art, an electronic flame-off device typically includes anelectrode (such as electrode 118) which is used to melt an end of a wireextending from a bonding tool (such as bonding tool 106) to form a freeair ball. As shown in FIG. 1E, gas flows through cavity 110 a aroundbonding tool 106 and adjacent the tip of electrode 118, therebyproviding the gas in the vicinity of the electronic flame-off operation(the gas flow is illustrated by the series of arrows).

Also shown in FIG. 1E is cavity 110 b. Cavity 110 b defines a gasdelivery path between (1) second gas inlet 116 (a gas supply pipe ortube 116), and (2) the vicinity of the bond site area of a wire bondingmachine. More specifically, as shown in FIG. 1E in by the arrows, gasflow (e.g., a controlled gas supply) is provided to second gas inlet116. The gas flows from second gas inlet 116 along the path provided bycavity 110 b. The path provided by cavity 110 a extends to a pluralityof through holes 110 b 3, 110 b 4, 110 b 5, 110 b 6, and 110 b 7. Asshown in FIG. 1E, gas flows through cavity 110 b, leading to (andthrough) through holes 110 b 3, 110 b 4, 110 b 5, 110 b 6, and 110 b 7.The gas then flows from through holes 110 b 3, 110 b 4, 110 b 5, 110 b6, and 110 b 7 downward toward the bond site area of the wire bondingmachine, thereby providing gas to the bond site area to reduce thepotential for oxidation of the wire and/or wire ends.

FIG. 1F is a front view of a portion of FIG. 1E taken along line 1E-1Ewhich illustrates top portion 110B and bottom portion 110A of gasdelivery mechanism 110. This sectional view provides a view of a portionof cavities 110 a and 110 b, as well as a view of a portion of throughholes 110 b 3 and 110 b 6. As shown in FIG. 1E, gas flows (as indicatedby the arrows) past through holes 110 b 3 and 110 b 6 toward bond sitearea 108 (device 120, to be wirebonded, is located at bond site area108).

As provided above, gas delivery mechanism 110 includes top portion 110Aand bottom portion 110A. FIGS. 1G-1H illustrate two variations of bottomportion 110B. As shown in FIGS. 1G-1H, bottom portion 110B definesbottom portion 110 a 1 of cavity 110 a. Likewise, bottom portion 110Bdefines bottom portion 110 b 1 of cavity 110 b (including through holes110 b 3, 110 b 4, 110 b 5, 110 b 6, and 110 b 7). Top portion 110B, notshown in FIGS. 1G-1H, defines corresponding portions of cavities 110 aand 110 b). Further, bottom portion 110A defines aperture portion 110 c1 of aperture 110 c configured to receive bonding tool 106 (e.g., seeFIG. 1B) (top portion 110B, not shown, defines a corresponding portionof aperture 110 c). Also shown in FIGS. 1G and 1H are recesses A1, A2defined in bottom portion 110A. These recesses A1 and A2, in conjunctionwith corresponding recesses in top portion 11oB (not shown), receive gasinlets 114 and 116 (e.g., gas supply pipes 114 and 116). Gas inlets 114and 116 provide gas to cavities 110 a and 110 b, respectively. FIGS.1G-1H also illustrate two different configurations for the tip end ofelectrode 118. That is, in FIG. 1G insulator 120 (e.g., an insulativebushing made of ceramic or the like) is provided at the tip end ofelectrode 118. Insulator 120 is provided to direct the spark fromelectrode 118 towards the end of the wire to form a free air ball (thewire is not shown in FIG. 1G). More specifically, the spark is directedfrom the very tip of electrode 118 as opposed to some point fartheralong the length of electrode 118. Further, an insulative sealant oradhesive may be provided at the opening of insulator 120 which receivesthe tip end of electrode 118 to further direct the spark. In contrast,in FIG. 1H, the tip end of electrode 118 is not received by an insulatorsuch as insulator 120.

While the exemplary embodiments of the present invention illustrated inFIGS. 1A-1H includes two gas supply sources (i.e., gas provided throughgas inlets/pipes 114 and 116), it is understood that a single gas supplysource/pipe could supply gas to gas supply mechanism 110.

As described above with respect to FIGS. 1A-1L, a gas delivery mechanismfor providing gas (1) in the vicinity of the electronic flame offoperation of a wire bonding machine, and (2) in the vicinity of the bondsite area of a wire bonding machine, is provided. However, the presentinvention is not limited to the configuration shown in FIGS. 1A-1H. Infact, there are multiple configurations contemplated within the scope ofthe present invention. Various additional exemplary configurations areillustrated in FIG. 2; FIG. 3; FIGS. 4A-4B; FIGS. 5A-5C, FIGS. 6A-6E,and FIGS. 7A-7E.

Referring to FIG. 2, bottom portion 210A of a gas delivery mechanism isillustrated (the top portion, which acts in a manner similar to topportion 110B described above, is omitted for simplicity). A gas deliverycavity is defined in the gas delivery mechanism, with the cavity beingpartially defined by bottom cavity portion 210 a 1 (and also by the topportion, not shown). Bottom portion 210A receives gas from gas inlet 214(e.g., gas supply pipe 214). A tip end of electrode 218 extends intoarea 210 c 1 where the flame-off operation for forming free air balls isto be conducted. Bottom portion 210A also defines apertures 210 a 3, 210a 4, 210 a 5, 210 a 6, 210 a 7, and 210 a 8. When gas is delivered tothe gas delivery mechanism via gas inlet/pipe 214, the gas extendsthrough the cavity and to: (1) area 210 c 1 for forming free air balls,where the gas travels from the cavity to area 210 c 1 through apertures212 a and 212 b, and (2) the bond site area via apertures 210 a 3, 210 a4, 210 a 5, 210 a 6, 210 a 7, and 210 a 8.

Referring to FIG. 3, the bottom portion 310A of a gas delivery mechanismis illustrated (the top portion, which acts in a manner similar to topportion 110B described above, is omitted for simplicity). A gas deliverycavity is defined in the gas delivery mechanism, with the cavity beingpartially defined by bottom cavity portion 310 a 1 (and also by the topportion, not shown). Bottom portion 310A receives gas from gas supplyinlet 314 (e.g., gas supply pipe 314). Electrode 318 extends through gasinlet/pipe 314, and the tip end of electrode 318 extends into area 310 c1 where the flame-off operation for forming free air balls is to beconducted. Bottom portion 310A also defines apertures 310 a 3, 310 a 4,310 a 5, 310 a 6, 310 a 7, and 310 a 8. When gas is delivered to the gasdelivery mechanism via gas inlet/pipe 314, the gas extends through thecavity and to: (1) area 310 c 1 for forming free air balls, where thegas travels from the cavity to area 310 c 1 through apertures 312 a and312 b and (2) the bond site area via 310 a 3, 310 a 4, 310 a 5, 310 a 6,310 a 7, and 310 a 8.

FIGS. 4A-4B illustrate gas delivery mechanism 410. Gas deliverymechanism 410 includes top portion 410A and bottom portion 410B whichcollectively define an internal cavity for receiving gas from gasinlet/supply pipe 414. Gas delivery mechanism 410 includes anchoringstructure 420 for anchoring gas delivery mechanism 410 to a supportstructure of the wire bonding machine. A tip end of electrode 418extends to area 410 c 1 for forming free air balls. Bottom portion 410Bdefines apertures 410 a 3, 410 a 4, 410 a 5, 410 a 6, 410 a 7, 410 a 8,410 a 9 and 410 a 10. When gas is delivered to the gas deliverymechanism 410 via gas inlet/pipe 414, the gas extends through theinternal cavity and to: (1) the area 410 c 1 for forming free air balls,where the gas travels from the cavity to area 210 c 1 through aperture414 a (see arrows indicating gas flow), and (2) the bond site area via410 a 3, 410 a 4, 410 a 5, 410 a 6, 410 a 7, 410 a 8, 410 a 9 and 410 a10. Gas delivery mechanism 410 also defines side opening 430 whichallows, for example, access for an operator and/or for a wire bondingtool to be positioned (e.g., swung or otherwise moved) adjacent area 410c 1 for forming free air balls.

FIGS. 5A-5C illustrate certain components of a wire bonding machine inconnection with gas delivery mechanism 510 (e.g., including a tapered orfunnel-shaped body portion). More specifically, transducer 504 (e.g., anultrasonic transducer) holds bonding tool 506. A tip end of bonding tool506 is configured to extend through aperture 510 c of gas deliverymechanism 510 (as shown in FIGS. 5A-5C) for formation of free air balls.Gas supply pipe 514 supplies gas to gas delivery mechanism 510 viaaperture 510 b. A tip end of electrode 518 extends into a free air ballforming area of gas delivery mechanism 510 via aperture 510 a. When gasis delivered to the gas delivery mechanism 510 via gas delivery pipe514, the gas extends to: (1) the area inside gas delivery mechanism 510for forming free air balls, and (2) the bond site area via the enlargedopening at the bottom of gas delivery mechanism 510 (as illustrated inFIG. 5B). The funnel-shaped sidewalls of gas delivery mechanism 510 aretapered, and aperture 510 c at the top of gas delivery mechanism 510 issmaller than the large opening at the bottom of gas delivery mechanism510 (See FIG. 5C where diameter D1 is clearly smaller than diameter D2).Thus, gas that is ejected from gas delivery mechanism 10 will mostlyexit through the enlarged opening at the bottom, and not throughaperture 510 c. This is particularly true when bonding tool 506 extendsthrough aperture 510 c, thereby partially blocking potential gas escapethrough aperture 510 c.

FIGS. 6A-6D illustrate various views of a portion of gas deliverymechanism 610, and other portions of a wire bonding machine similar tothose shown in FIGS. 1A-1H. More specifically, the wire bonding machineincludes device clamp 602, transducer 604, bonding tool 606, and gasdelivery mechanism 610. Also shown in FIGS. 6A-6D is electrode 618,where a tip of electrode 618 extends through aperture 618 a of gasdelivery mechanism 610. Gas delivery mechanism 610 defines taperedthrough hole 610 c which is configured to receive bonding tool 606during a wire bonding operation. In this exemplary embodiment of thepresent invention, through hole 610 c is the free air ball formationarea. More specifically, during formation of a free air ball, an end ofa wire extending from bonding tool 606 is positioned in the free airball formation area (i.e., in through hole 610 c). A tip end ofelectrode 618, which is used to form a free air ball on the end of thewire, is also positioned in the free air ball formation area. A covergas is provided via gas inlet 614, and the cover gas travels throughcavity/path 622 and exits at gas outlet 622 a into through hole 610 c.Thus, the cover gas provides protection against oxidation during theformation of free air balls in through hole 610 c.

During a wire bonding operation bonding tool 606 extends furtherdownward into (and at least partially past) through hole 610 c to formwire bumps or wire loops on a device to be wirebonded at the bond sitearea. The cover gas that was ejected from gas outlet 622 a into throughhole 610 c tends to travel downward through the lower opening of throughhole 610 c to bond site area. More specifically, because through hole610 is tapered, the diameter of through hole 610 c is smaller at the topof gas delivery mechanism 610 when compared to the diameter of thethrough hole at the bottom (i.e., diameter D1 is smaller than diameterD2 in FIG. 6D). Thus, more cover gas would tend to exit through hole 610c at the bottom than at the top. Additionally, during certain portionsof the wire bonding operation bonding tool 606 will block a largeportion of the upper portion of through hole 610 c, thus substantiallyreducing the potential for the escape of cover gas through the top ofthrough hole 610 c. Thus, it is clear that a large portion of the covergas that exits through hole 610 c will be directed downward toward thebond site area, thus providing further protection from oxidation duringthe wire bonding operation.

FIGS. 7A-7E illustrates another gas delivery mechanism 710 (andcorresponding portions of a wire bonding machine) that operates verysimilar to the mechanism 610 shown in FIGS. 6A-6D. More specifically,the wire bonding machine includes device clamp 702, transducer 704,bonding tool 706, electrode 718 (including a tip portion extendingthrough aperture 718 a), and gas delivery mechanism 710. Gas deliverymechanism 710 defines through hole 710 c (i.e., free air ball formationarea 710 c) which is configured to receive bonding tool 706 during awire bonding operation. A cover gas is provided via gas inlet 714, andthe cover gas travels through cavity/path 722 and exits at gas outlet722 a into through hole 710 c to provide cover gas to protect againstoxidation during free air ball formation. As described above withrespect to FIGS. 6A-6D, because through hole 710 is tapered (and becauseof the partial blockage of the top portion of through hole 710 c bybonding tool 706) more cover gas would tend to exit through hole 710 cat the bottom than at the top, thereby providing cover gas directedtoward the bond site area.

FIGS. 7A-7E also illustrate an additional gas inlet 716 which provides acover gas through cavity/path 624, exiting gas delivery mechanism 710 atgas outlet 624 a. Gas outlet 624 a is provided on a bottom surface ofgas delivery mechanism 710 such that the exiting cover gas is directedtoward a bond site area of the wire bonding machine. Thus, in contrastto the exemplary embodiment of the present invention shown in FIGS.6A-6D (where the cover gas provided to the bond site area was the samecover gas provided to free air ball formation area 610 c, which exitedarea 610 c through a bottom portion of area 610 c), gas deliverymechanism 710 also includes an additional source of cover gas to thebond site area via gas inlet 616, cavity/path 624, and gas outlet 624 a.Thus, additional protection (in addition to the protection provided bythe gas extending downward out of the free air ball formation area)against potential oxidation at the bond site area is provided.

The various exemplary gas delivery mechanisms disclosed herein may besupported by various structures of a wire bonding machine, for example,the bond head of a wire bonding machine. For example, the gas deliverymechanisms may be supported by the EFO structure, amongst others.

The various exemplary gas delivery mechanisms disclosed herein may beformed from a number of different materials. While metals (e.g.,stainless steel) are contemplated, because of the close proximity of thegas delivery mechanism to the sparking from the EFO electrode, it may bedesirable to form the body of the gas delivery mechanism from aninsulative, and perhaps heat resistant, material such as ceramic,polyimide, amongst others.

The flow of cover gas from a gas supply source (e.g., via a gas supplytube/pipe or the like) may be a continuous flow of cover gas during theentire wire bonding operation. Alternatively, the flow may be acontrolled flow (e.g., controlled using a controller integrated with thewire bonding machine) that is provided, for example, during periods ofgreatest concern regarding potential oxidation (e.g., during free airball formation, etc.).

The drawings provided herein illustrate exemplary structures fordirecting a cover gas to (1) the vicinity of the electronic flame offoperation of a wire bonding machine, and (2) the vicinity of the bondsite area of a wire bonding machine; however, the invention is notlimited to the illustrated configurations. The present inventioncontemplates any type of structure, system or process for providingcover gas to both (1) the vicinity of the electronic flame off operationof a wire bonding machine, and (2) the vicinity of the bond site area ofa wire bonding machine. Further, the gas delivery mechanism can includeany number of gas inlets (e.g., inlet gas pipes) to provide the desiredgas flow and distribution to the free air ball formation area and thebond site area.

When the present invention is used in connection with a wire formed of areactive metal (e.g., copper, aluminum, etc.) the cover gas is desirablynon-reactive with the metal and may be reducing. For example, the covergas may be an effectively inert gas such as nitrogen or argon. Areducing gas (e.g., hydrogen) may be added to react with any oxygen thatmay be present; however, the cover gas system of the present inventionmay be utilized to exclude air from the bond site area without the needfor hydrogen in the cover gas. This is a further advantage of thepresent invention because of the difficulties of using large quantitiesof highly flammable hydrogen.

The teachings of the present invention may also be utilized inconnection with non-reactive bonding wire, such as gold wire. Forexample, the cover gas may be utilized to provide a shield of clean gasat the bond site area, thereby providing a desirable environment forformation of gold wire loops.

Although the present invention has been described primarily with respectto cover gases such as nitrogen and argon (with or without a forming gassuch as hydrogen), it is not limited thereto. Any gas may be utilized solong as it does not react undesirably with the metal used as a bondingwire.

It is understood that the present invention may be applicable to a wirebonding machine that forms wire loops, a wire bonding machine that formsconductive bumps (a bumping machine or a wafer bumping machine), amachine that forms both wire loops and conductive bumps, etc.

Although the invention is illustrated and described herein withreference to specific embodiments, the invention is not intended to belimited to the details shown. Rather, various modifications may be madein the details within the scope and range of equivalents of the claimsand without departing from the invention.

1. A wire bonding machine comprising: a bonding tool; an electrode forforming a free air ball on an end of a wire extending through thebonding tool, the free air ball being formed at a free air ballformation area of the wire bonding machine; a bond site area for holdinga semiconductor device during a wire bonding operation; and a gasdelivery mechanism configured to provide a cover gas to: (1) the bondsite area whereby the cover gas is ejected through at least one apertureof the gas delivery mechanism to the bond site area, and (2) the freeair ball formation area.
 2. The wire bonding machine of claim 1 whereinthe gas delivery mechanism defines a through hole from a top surface ofthe gas delivery mechanism to a bottom surface of the gas deliverymechanism, the through hole being configured to receive the bonding toolduring a wire bonding operation.
 3. The wire bonding machine of claim 2wherein the through hole defined by the gas delivery mechanism includesthe free air ball formation area.
 4. The wire bonding machine of claim 3wherein the through hole is tapered.
 5. The wire bonding machine ofclaim 4 wherein a diameter of the tapered through hole at the topsurface is larger than a diameter of the tapered through hole at thebottom surface.
 6. The wire bonding machine of claim 4 wherein adiameter of the tapered through hole at the bottom surface is largerthan a diameter of the tapered through hole at the top surface.
 7. Thewire bonding machine of claim 3 wherein the gas delivery mechanismincludes a first gas inlet, the first gas inlet providing the cover gasto the free air ball formation area, whereby at least a portion of thecover gas provided by the first gas inlet exits the free air ballformation area and is directed toward the bond site area.
 8. The wirebonding machine of claim 7 wherein the gas delivery mechanism includes asecond gas inlet, the second gas inlet providing cover gas to a cavitydefined by the gas delivery mechanism, the cavity being distinct fromthe free air ball formation area, whereby at least a portion of thecover gas provided by the second gas inlet exits the cavity and isdirected toward the bond site area.
 9. The wire bonding machine of claim1 wherein the at least one aperture of the gas delivery mechanismincludes a plurality of apertures through which the cover gas is ejectedtoward the bond site area.
 10. The wire bonding machine of claim 9wherein the plurality of apertures are defined by a bottom surface ofthe gas delivery mechanism.
 11. The wire bonding machine of claim 1wherein the gas delivery mechanism defines (1) a first cavity forreceiving the cover gas from at least one gas inlet and for providingthe cover gas to the bond site area through the at least one aperture,and (2) a second cavity for receiving the cover gas from the at leastone gas inlet and for providing the cover gas to the free air ballformation area.
 12. The wire bonding machine of claim 11 wherein the atleast one gas inlet includes a first gas inlet for providing the covergas to the first cavity, and a second gas inlet for providing the covergas to the second cavity.
 13. The wire bonding machine of claim 1further comprising a device clamp for securing the semiconductor deviceduring the wire bonding operation, the device clamp defining a deviceaperture through which the bonding tool can access the semiconductordevice to perform the wire bonding operation at the bond site area, thewire bonding machine further comprising a cover for covering at least aportion of the device aperture during the wire bonding operation. 14.The wire bonding machine of claim 1 wherein the electrode extendsthrough a portion of the gas delivery mechanism such that a tip of theelectrode is positioned at the free air ball formation area.
 15. Thewire bonding machine of claim 14 further comprising an insulatorsurrounding a portion of the tip of the electrode adjacent the free airball formation area.
 16. The wire bonding machine of claim 1 wherein thegas delivery mechanism includes a gas inlet for receiving the cover gasfrom a gas supply, and wherein the electrode extends through the gasinlet.
 17. The wire bonding machine of claim 1 wherein the gas deliverymechanism defines a side opening such that sidewalls of the gas deliverymechanism do not entirely surround the bonding tool during the wirebonding operation.
 18. The wire bonding machine of claim 1 wherein thegas delivery mechanism includes a funnel shaped body portion defining(1) a first opening at a top of the funnel shaped body portion toreceive the bonding tool, and (2) a second opening at a bottom of thefunnel shaped body portion for ejection of the cover gas toward the bondsite area.
 19. The wire bonding machine of claim 18 wherein the firstopening has a smaller diameter than a diameter of the second opening.20. The wire bonding machine of claim 19 wherein the second opening hasa smaller diameter than a diameter of the first opening.
 21. The wirebonding machine of claim 18 wherein the funnel shaped body portionincludes tapered sidewalls such that a diameter of the funnel shapedbody portion is larger at the top as compared to a diameter at thebottom of the body portion.